1. Field of the Invention
The present invention relates to a projection optical system for a projection exposure apparatus to be employed when a semiconductor element or a liquid crystal display element is to be manufactured by the photolithographic process, a projection exposure apparatus provided with the projection optical system, Projection Method thereof, Exposure Method thereof and Fabricating Method for fabricating a device using the projection exposure apparatus, and, more particularly, to a projection optical system for a scanning type projection exposure apparatus and having a resolution of 0.1 microns or less in an ultraviolet region
2. Related Background Art
In the photolithographic process for manufacturing a semiconductor element or the like, there has been employed a projection exposure apparatus for projecting and exposing a pattern image formed on a photo mask or reticle (as will be generally called the xe2x80x9creticlexe2x80x9d), through a projection optical system to a wafer or glass plate to which a photoresist or the like is applied. As the degree of integration of the semiconductor element or the like grows higher, there rises higher the resolution which is demanded for the projection optical system employed in the projection exposure apparatus. In order to satisfy this demand, it is necessary to shorten the wavelength of an illumination radiation (or exposure radiation) and to enlarge the numerical aperture (as will be abbreviated into the xe2x80x9cNAxe2x80x9d) of the projection optical system, or to effect the-both. When the illumination radiation has a wavelength of 180 nm or less, for example, it is possible to achieve a high resolution of 0.1 microns or less.
As the wavelength of the illumination radiation is the-shorter, the kind of a practical glass material is the-more limited by the optical absorption. Especially when the wavelength is as short as 180 nm or less, what can be practiced as the glass material is limited to only fluorite. When the wavelength is shorter than 100 nm, moreover, there is no glass material to be employed as the refractive lens. It is, therefore, necessary to develop an optical system employing no refractive lens or only an extremely small number of refractive lenses.
Several techniques for constructing the projection optical system have been proposed by the reflection type optical system employing no refractive lens or the reflection type optical system employing an extremely small number of refractive lenses. For example, an optical system having an aperture as large as the NA exceeding 0.2 on the image side has been disclosed in U.S. Pat. Nos. 5,815,310 and 5,686,728.
However, the optical systems disclosed are not sufficiently corrected in aberration when the numerical aperture on the image side exceeds 0.3 and when an emitted radiation in a soft X-ray range of a wavelength of 100 nm or less is used. Therefore, the optical systems thus far described cannot provide a sufficient optical performance if employed as the projection optical system having a resolution of 30 nm or less.
The object of the invention is to provide a projection optical system having a large numerical aperture in a soft X-ray wavelength range of 200 nm or less, specifically 100 nm or less and a resolution drastically lower than 50 nm, and a projection exposure apparatus provided with the projection optical system.
In order to solve the above-specified problem, according to the invention, there is provided a projection optical system for projecting the image of a first plane on a second plane, comprising: an arcuate field area spaced away from the optical axis of the projection optical system; and a shading area in a pupil plane of the projection optical system.
In the invention, on the other hand, the projection optical system further comprises: a first imaging optical system for forming an intermediate image of said first plane; and a second imaging optical system for forming the final image of said first plane on said second plane on the basis of an emitted radiation from said intermediate image. Said first imaging optical system includes at least two reflecting surfaces, and said second imaging optical system includes at least one reflecting surface having an optically transmissive portion.
In the invention, on the other hand, said shading area has a ring shape (doughnut shape).
According to the invention, on the other hand, there is provided a projection optical system for projecting the image of a first plane on a second plane, comprising: a first imaging optical system for forming an intermediate image of said first plane; and a second imaging optical system for forming the final image of said first plane on said second plane on the basis of an emitted radiation from said intermediate image, wherein said first imaging optical system includes at least two reflecting surfaces, and said second imaging optical system includes at least one reflecting surface having an optically transmissive portion.
In the invention, on the other hand, the projection optical system further comprises: a first imaging optical system for forming an intermediate image of said first plane; and a second imaging optical system for forming the final image of said first plane on said second plane on the basis of an emitted radiation from said intermediate image, wherein said first imaging optical system includes at least one reflecting surface of a positive power, and at least one reflecting surface of a negative power, wherein said second imaging optical system includes a primary mirror disposed in the vicinity of said intermediate image, and an auxiliary mirror disposed closer to said second plane than said primary mirror, wherein said primary mirror has a first optically transmissive portion and a first reflecting surface of a positive power (a concave shape), and wherein said auxiliary mirror has a second optically transmissive portion and a second reflecting surface, whereby: the emitted radiation from said intermediate image is reflected through said first optically transmissive portion of said primary mirror on said second reflecting surface of said auxiliary mirror; the emitted radiation, as reflected on said second reflecting surface of said auxiliary mirror, is reflected on said first reflecting surface of said primary mirror; and the emitted radiation, as reflected on said first reflecting surface of said primary mirror, is transmitted through said second optically transmissive portion of said auxiliary mirror to form said final image on said second plane. Further, the power on the reflecting surface is an inverse number of a focal distance of said reflecting surface.
In the invention, on the other hand, all the optical elements composing said projection optical system are reflecting surfaces.
In the invention, on the other hand, the projection optical system further comprises: a first imaging optical system for forming an intermediate image of said first plane; and a second imaging optical system for forming the final image of said first plane on said second plane on the basis of an emitted radiation from said intermediate image, wherein said first imaging optical system includes at least one refractive lens component, and wherein said projection optical system is a telecentric optical system on the sides of said first plane and said second plane.
In the invention, on the other hand, all the optical elements composing said projection optical system are positioned to have their optical axes on a common straight line.
In the invention, on the other hand, the projection optical system further comprises: a first imaging optical system for forming an intermediate image of said first plane; and a second imaging optical system for forming the final image of said first plane on said second plane on the basis of an emitted radiation from said intermediate image, wherein said projection optical system is a telecentric optical system on the side of said second plane, and wherein a shading member for forming said shading area is arranged in the vicinity of a pupil plane in said first imaging optical system.
In the invention, on the other hand, the projection optical system further comprises a first imaging optical system for forming an intermediate image of said first plane; and a second imaging optical system for forming the final image of said first plane on said second plane on the basis of an emitted radiation from said intermediate image, wherein said first imaging optical system includes a reflecting mirror arranged in the vicinity of the pupil plane, and wherein the reflecting surface of said reflecting mirror includes a reflective area having a predetermined reflectivity, and a low reflectivity area having a lower reflectivity than that of said reflective area. Here, the low reflectivity area includes an area (non-reflective area) which does not reflect the emitted radiation, thereby the shape of the shading area on the pupil plane is substantially equal among the pupil planes corresponding to the emitted radiation from any of positions of the field area.
According to the invention, there is provided a projection exposure apparatus for projecting and transferring the image of a mask having a predetermined pattern to a photosensitive substrate, comprising: a radiation source for feeding an emitted radiation of a predetermined wavelength; a projection optical system according to the above invention; a first stage for positioning said mask on said first plane; and a second stage for positioning said photosensitive substrate on said second plane.
Here, the invention is preferred to have any of the following constructions (1) to (5):
(1) It is preferable that said projection optical system has at least two aspherical reflecting surfaces;
(2) It is preferable that the field stop is disposed in the vicinity of said intermediate image;
(3) It is preferable that said projection optical system has a reflecting surface and that a substrate having said reflecting surface has a linear expansion coefficient of 3 ppm/xc2x0 C. or less;
(4) It is preferable that said projection optical system includes a primary mirror having a first optically transmissive portion and a first reflecting surface, and an auxiliary mirror having a second optically transmissive portion and a second reflecting surface, that an aperture stop is disposed between said primary mirror and said auxiliary mirror, that the emitted radiation having passed through said first optically transmissive portion of said primary mirror is reflected on the second reflecting surface of said auxiliary mirror, that the emitted radiation reflected on said second reflecting surface of said auxiliary mirror is reflected on the first reflecting surface of said primary mirror, and that the emitted radiation reflected on the said first reflecting surface of said primary mirror is guided through said second optically transmissive portion of said auxiliary mirror to form said final image on said second plane; and
(5) It is preferable that there are included a primary mirror having a first optically transmissive portion and a first reflecting surface and an auxiliary mirror having a second optically transmissive portion and a second reflecting surface, and that a shading member is arranged between said primary mirror and said auxiliary mirror.
In the invention, on the other hand, it is preferable that said first optically transmissive portion is formed in an area surrounded by the area of said first reflecting surface, and that said second optically transmissive portion is formed in an area surrounded by the area of said second reflecting surface.
According to another aspect of the invention, on the other hand, there is provided a projection optical system for projecting the image of a first plane on a second plane, comprising: a primary mirror including a first optically transmissive portion and a first reflecting surface formed in an area surrounding said first optically transmissive portion; and an auxiliary mirror including a second optically transmissive portion and a second reflecting surface formed in an area surrounding said second optically transmissive portion, wherein said first and second reflecting surfaces form at least three optical paths between said first and second reflecting surfaces, and wherein said first and second optically transmissive portions are formed at a position which does not contain an optical axis formed by said first and second reflecting surfaces.
According to another aspect of the invention, on the other hand, there is provided a projection optical system for projecting the image of a first plane on a second plane, comprising: a primary mirror including a first optically transmissive portion and a first reflecting surface formed in an area surrounding said first optically transmissive portion; and an auxiliary mirror including a second optically transmissive portion and a second reflecting surface formed in an area surrounding said second optically transmissive portion, wherein said first and second reflecting surfaces are formed at a position which contains an optical axis formed by said first and second reflecting surfaces, and wherein said first and second optically transmissive portions are formed at a position which does not contain said optical axis.
It is preferable that any of the aforementioned constructions further comprises a reflecting mirror having a reflecting surface at a position spaced away from said optical axis. In this case, moreover, it is preferable that said reflecting mirror is arranged on the side of said first plane of said primary mirror and said auxiliary mirror.
On the other hand, it is preferable that any of the aforementioned constructions comprises a shading member for shading the emitted radiation which passes not through said first and second reflecting surfaces but through said first and second optically transmissive portions.
According to the invention, on the other hand, there is provided a projection exposure apparatus for projecting and transferring the image of a mask having a predetermined pattern to a photosensitive substrate, comprising: a radiation source for feeding an emitted radiation of a predetermined wavelength; a projection optical system of the present invention; a first stage for positioning said mask on said first plane; and a second stage for positioning said photosensitive substrate on said second plane.
On the other hand, said projection exposure apparatus is preferred to have any of the following constructions (6) to (10):
(6) It is preferable that said mask is of a reflection type for selectively reflecting said emitted radiation selectively:
(7) It is preferable in the present invention or said construction (6) that said radiation source feeds an emitted radiation of 200 nm or less;
(8) It is preferable in said construction (7) that said radiation source feeds an emitted radiation of 160 nm or less;
(9) It is preferable in said construction (8) that said radiation source feeds an emitted radiation of 100 nm or less; and
(10) It is preferable in the present invention or any of said constructions (6) to (9) that said first stage is disposed to move in a direction across the longitudinal direction of said arcuate field of view, and that said second stage is disposed to move in a direction across the longitudinal direction of the final image of said arcuate field of view.
According to the invention, on the other hand, there is provided a projection exposure method for projecting and transferring the image of a mask having a predetermined pattern to a photosensitive substrate, comprising: preparing a projection optical system according to-the present invention or any of said constructions; arranging said mask on said first plane of said projection-optical system; arranging said-photosensitive substrate on said second plane of said projection optical system; and feeding an emitted radiation of a predetermined wavelength to said mask arranged on said first plane, thereby to form the image of said mask on said photosensitive substrate arranged on said second plane.
It is preferable that said projection exposure method has any of the following constructions (11) to (16):
(11) It is preferable that said emitted radiation is reflected on said mask and guided to said projection optical system;
(12) It is preferable that an emitted radiation of a wavelength of 200 nm or less is fed to said mask;
(13) It is preferable in said item (12) that an emitted radiation of a wavelength of 160 nm or less is fed to said mask;
(14) It is preferable in said item (13) that an emitted radiation of a wavelength of 100 nm or less is fed to said mask;
(15) It is preferable in any of the aforementioned items that the projection exposure is performed while changing the relative positions between said photosensitive substrate and said projection optical system; and
(16) It is preferable in said item (15) that the direction to change said position crosses the longitudinal direction of said arcuate field of view of said projection optical system.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.